This invention relates to apparatus for entraining and directing a wet paper web particularly for use in a paper making process.
In paper making a pulp is laid on a wire or grid to a required thickness and over a width which can be the order of 10 feet. The wire or grid is continually moving pass the point of deposit or laying of the pulp and carries the wet pulp while water is initially drained from the pulp to form a soft very fragile layer which will eventually become the paper. After leaving the wire, the pulp is initially carried around a first roller or granite on which it is squeezed and from which it is transferred in the wide web to a drying zone. The web is carried through the drying zone on rope pulleys arranged at the outside edges of the web with the web suspended across the space between the pulleys.
Subsequent to drying the web can be passed through a number of calendar roller stacks to yet further compress the paper and form effectively the finished product.
In many systems for manufacturing paper in this manner, there are spaces between the various components over which the web must traverse. While the line is running normally this continues without problems in that the web has sufficient continuity in strength to span the space. However should a break occur in the web or upon start up of a shift, it is necessary to feed the web from one position to the next across the space between the various items.
Initially such transfer of the web has been carried out by hand in that a first narrow strip of the web is formed at a roller and is then grasped and manually transferred from a roller to the next position in line. Once the narrow strip is set up and running properly, the narrow strip is gradually increased in width until the whole web is running in the proper manner under the proper tension.
This manual technique is of course very difficult, time consuming and dangerous.
Various devices has therefore been developed to assist the transfer and particularly U.S. Pat. Nos. 3,999,696, 4,014,487, 4,136,808, 4,147,287 and 4,186,860 (Imants Reba, assigned to Crown Zellerbach Corporation) show arrangements of this type which use the Coanda effect developed by an airfoil to entrain and transfer the material over a directional surface to the next position in line. These Patents have resulted in a machine currently available on the market which is used for transfer of the paper web at the dry end of the machine that is after the dryer and the calendar roll stacks where the paper web is relatively strong and easy to control. Attempts have been made to manufacture a product of this type which is suitable for transfer of the web at the wet end of the process or machine where the web is effectively merely a compressed layer of pulp and thus has very little strength. All attempts to date have been unsuccessful and there remains therefore a major requirement for a device of this type which can transfer the paper web at the wet end of the machine.